The invention related generally to work vehicles, such as skid steer loaders and other skid steer vehicles. More particularly, it relates to drive and suspension systems for such vehicles.
Skid steer vehicles such as skid steer loaders are used in a wide variety of construction environments where they are particularly suitable due to their small size and maneuverability.
Skid steer vehicles can turn with an effective turning radius of zero. They can rotate about a vertical axis extending through the center of the chassis by driving the wheels on one side of the vehicle forward and the wheels on the other side of the vehicle backwards. Since the wheels cannot be steered with respect to the chassis, this causes the wheels to skid sideways as they rotate. This is the extreme case. Even when the vehicle is moving forward or backward (i.e. the wheels on both sides of the vehicle are driven in the same direction) the vehicle still steers by skidding, albeit to a lesser degree.
Skid steer vehicles are well suited to work on construction sites and even within buildings due to this ability to skid steer. Enhancing this capability is their compact size.
Skid steer vehicles have not been provided with sprung suspensions for several reasons.
First, the addition of a suspension is difficult due to the compact size of the skid steer vehicle itself. Adding suspensions would increase the width of the vehicle and make it less suitable for the close spaces in which it is used.
Second, traditional automotive-type suspensions would cause excessive pitching of the work vehicle, given its short wheelbase (e.g. vehicles having a front-to-rear wheel spacing of less than two wheel diameters). For example, a typically automotive or truck type suspension includes a vertically oriented spring that is coupled to the chassis at its upper end. The point of coupling is typically directly above the rotational axis of the wheel supported on that suspension. As a result, whenever the wheel is forced upward, (such as when the car goes over a bump) the spring is compressed, and an upward force is applied to the chassis directly above the wheel where the spring is anchored.
For a vehicle such as a car with a large wheel-to-wheel spacing (i.e. a fore-and-aft wheel spacing of six wheel diameters or more) and a long wheelbase, this upward force does not cause significant pitching in the vehicle. For a vehicle such as a skid steer loader, with its small wheel-to-wheel spacing (i.e. a fore-and-aft wheel spacing of less than two wheel diameter) and short wheelbase, the pitching would be more severe.
What is needed therefore is a suspension system for a skid steer loader that provides springing, but avoids or reduces the pitching inherent in a short wheelbase vehicle having a spring coupled to the chassis adjacent the wheel. It is an object of this invention to provide such a vehicle.
In accordance with a first embodiment of the invention a skid steer vehicle is provided that includes a chassis having a left side and a right side; an engine fixed to the chassis; a first hydraulic fluid pump driven by the engine to provide hydraulic fluid under pressure; a second hydraulic fluid pump driven by the engine to provide hydraulic fluid under pressure; at least a first hydraulic motor in fluid communication with the first hydraulic fluid pump; at least a second hydraulic motor in fluid communication with the second hydraulic fluid pump; left front and left rear suspensions mounted in a fore-and-aft arrangement on the left side of the chassis for pivotal movement with respect thereto, each left suspension including a left ground-engaging wheel extending from the left side of the chassis and rotationally coupled to the at least a first hydraulic motor to be driven in rotation thereby, a left control arm assembly coupled to and between the left wheel and the chassis to pivot with respect to the chassis about a left control arm pivotal axis; and right front and right rear suspensions mounted in a fore-and-aft arrangement on the right side of the chassis for pivotal movement with respect thereto, each right suspension including a right ground-engaging wheel extending from the right side of the chassis and rotationally coupled to the at least a second hydraulic motor to be driven in rotation thereby, a right control arm coupled to and between the right wheel and the chassis to pivot with respect to the chassis about a right control arm pivotal axis, wherein said at least a first hydraulic motor is coupled to both of the left side suspension wheels to drive the left side wheels at the same speed, and wherein said at least a second hydraulic motor is coupled to both of the right side suspension wheels to drive the right side wheels at the same speed.
Each of the control arms of the left side suspensions and the right side suspensions may be pivotally coupled to the chassis about a pivotal axis that is disposed closer to the center of gravity of the vehicle than wheel coupled to said each control arm. The left control arm pivotal axis of the left front suspension and the right control arm pivotal axis of the right front suspension may extend laterally with respect to the chassis and may be located behind and parallel to the rotational axis of the left front and right front wheels, respectively. The left front suspension may further include a left front spring coupled to the left front control arm at the left front control arms"" pivotal axis to apply a torsional force thereto, wherein the left front spring is coupled to the chassis at a position closer to the center of gravity of the vehicle than the left front control arm; and a right front spring coupled to the right front control arm at the right front control arms"" pivotal axis to apply a torsional force thereto, wherein the right front spring is coupled to the chassis at a position closer to the center of gravity of the vehicle than the left front control arm. The left front spring and the right front spring may be torsion bars extending laterally with respect to the chassis and behind the rotational axes of the left front suspension wheel and the right front suspension wheel. The left rear suspension may further include a left rear spring coupled to the left rear control arm at the left rear control arms"" pivotal axis to apply a torsional force thereto. The left rear spring may be coupled to the chassis at a position closer to the center of gravity of the vehicle than the left rear control arm. A right rear spring may be coupled to the right rear control arm at the right rear control arms"" pivotal axis to apply a torsional force thereto. The right rear spring may be coupled to the chassis at a position closer to the center of gravity of the vehicle than the left rear control arm.
In accordance with a second embodiment of the invention, a skid steer vehicle is provided that includes a chassis having a left side and a right side; an engine mounted on the chassis; first and second hydraulic pumps driven by the engine to provide first and second sources of hydraulic fluid under pressure; four independent suspensions coupled to the chassis, each suspension including a torsion bar having a longitudinal axis, a fixed end and a free end, wherein the fixed end is fixed with respect to the chassis, a control arm having first and second ends, wherein the first end is mounted to the chassis to pivot with respect to the chassis and further wherein the free end of the torsion bar is fixed to the first end of the control arm to pivot with respect to the chassis and thereby applying a torsional load to the torsion bar, a ground-engaging wheel rotationally mounted on the second end of the control arm to rotate with respect thereto, and a hydraulic motor fixed to the second end of the control arm and also coupled to the wheel to rotate the wheel with respect to the control arm.
Two of the four suspensions may be front suspensions, disposed one on each side of the chassis. Two of the four suspensions may be rear suspensions disposed one on each side of the chassis. The control arms of the two front suspensions may be coupled to the chassis on either side of the chassis in a central region thereof and may extend forward toward the front of the vehicle. The control arms of the two rear suspensions may be coupled to the chassis on either side of the chassis in the central region thereof and extend backward toward the rear of the vehicle. The longitudinal axes of the torsion bars of the front suspensions may be generally parallel and coaxial and the longitudinal axes of torsion bars of the rear suspensions may be generally are generally parallel and coaxial. The torsion bar of each of the two front suspensions may be fixed to the chassis at a point rearward of the rotational axis of its associated wheel, and the torsion bar of each of the two rear suspensions may be fixed to the chassis at a point forward of the rotational axis of its associated wheel. Each suspension may further include a reduction gear wheel hub that is mounted to the second end of the control arm and to which the wheel is fixed, the wheel hub being coupled to and driven by the hydraulic motor and including an integral reduction gear set to rotate the wheel at a velocity less than the rotational velocity of the hydraulic motor. The control arm of each of the suspensions may include at least two spaced apart steel plates extending generally perpendicular to the ground and defining a space therebetween in which the hydraulic motor is received and supported. The first hydraulic pump may be hydraulically connected to the two hydraulic motors of the suspensions disposed on the left side of the chassis in a first series circuit and the second hydraulic pump may be hydraulically connected to the two hydraulic motors of the suspensions disposed on the right side of the chassis in a second series circuit.
In accordance with a third embodiment of the invention, a skid steer vehicle is provided that includes a chassis having a left side and a right side; an engine mounted on the chassis; two independent suspensions disposed at the front of the vehicle, one on the left side of the chassis and one on the right side of the chassis, the front suspensions including a fore-and-aft oriented forward control arm that is pivotally coupled to the vehicle at an after end of the forward control arm, a ground-engaging forward wheel coupled to a forward end of the forward control arm and having a rotational axis about which the forward wheel rotates to convey the vehicle over the ground, and a forward torsion bar that is coupled to the after end of the forward control arm at a location rearward of the rotational axis of the forward wheel, the torsion bar extending laterally inward from the forward control arm generally toward the center of the vehicle to a forward suspension anchor point at which it is fixed to the chassis of the vehicle, wherein the forward suspensions anchor point is located to the rear of the forward wheel""s rotational axis and laterally inward from the forward wheel itself; and two independent suspensions disposed at the rear of the vehicle, one on the left side of the chassis and one on the right side of the chassis, the rear suspensions includingxcx9ca fore-and-aft oriented rear control arm that is pivotally coupled to the vehicle at a forward end of the rear control arm, a ground-engaging rear wheel coupled to a rearward end of the rear control arm and having a rotational axis about which the rear wheel rotates to convey the vehicle over the ground, and a torsion bar that is coupled to the forward end of the rear control arm at a location forward of the rotational axis of the rear wheel, the torsion bar extending laterally inward from the rear control arm generally toward the center of the vehicle to a rear suspension anchor point at which it is fixed to the chassis of the vehicle, wherein the rear suspension anchor point is located forward of the rear wheel""s rotational axis and laterally inward from the rear wheel itself.
Each torsion bar of the four suspensions may extend generally perpendicular to the longitudinal extent of the control arm to which it is coupled. Each of the four control arms may extend horizontally. The center of each wheel may be at the same height above the ground as the pivot point of the control arm to which it is coupled when the vehicle is stationary. Each control arm may include a pair of spaced-apart steel plates, each plate extending both in a vertical direction and in a fore-and aft direction. Each of the two front independent suspensions may include a fluid-filled shock-absorbing element that is coupled to and between the forward end of each suspension""s control arm and the chassis. Each of the two rear independent suspensions may include a fluid-filled shock-absorbing element that is coupled to and between the rearward end of each suspension""s control arm and the chassis. Each of the two front independent suspensions may include a hydraulic motor that is fixed to the forward end of the control arm of said each front suspension. Each of the two rear independent suspensions may include a hydraulic motor that is fixed to the rear end of the control arm of said each rear suspension.
In accordance with a fourth embodiment of the invention, a skid steer vehicle is provided including a chassis having a left side, a right side, and a center of gravity; an internal combustion engine mounted on the chassis; and left and right front suspensions pivotally coupled to and extending from the left and right sides of the chassis, respectively, wherein each front suspension includes a front wheel; a front control arm coupled to the front wheel, and pivotally coupled to the chassis at at least one pivot point defining a control arm to chassis pivotal axis, wherein the pivotal axis is disposed between the center of gravity of the vehicle and the front wheel, and a spring element coupled to and between the front control arm and the chassis to apply a torque to the front control arm, the spring element being fixed to the chassis at a point closer to the center of gravity of the vehicle than the pivot point of the front control arm.
The control arm to chassis pivotal axes may extend laterally with respect to the chassis. The spring element may be a torsion bar and may be coaxial with the front control arm to chassis pivotal axis. The front control arm may be an elongate member extending fore-and-aft with respect to the chassis. The front control arm may have a forward end and an after end, the forward end coupled to the front wheel and the after end pivotally coupled to the chassis. The front wheel may be coupled to the forward end of the front control arm to rotate with respect to the front control arm. The skid steer vehicle may further include a first hydraulic pump coupled to the engine to provide hydraulic fluid under pressure; at least one hydraulic motor coupled to the first pump and to the left front wheel to rotate the left front wheel; a second hydraulic pump coupled to the engine to provide hydraulic fluid under pressure; at least a second hydraulic motor coupled to the second pump and to the right front wheel to rotate the right front wheel. It may also include left and right rear suspensions pivotally coupled to and extending from the left and right sides of the chassis, respectively, wherein each rear suspension includes a rear wheel and a rear control arm coupled to the wheel, and pivotally coupled to the chassis at at least one pivot point defining a control arm to chassis pivotal axis, wherein the pivotal axis is disposed between the center of gravity of the vehicle and the rear wheel, and wherein the at least one hydraulic motor is coupled to the left rear wheel to rotate the left rear wheel at the same velocity as it rotates the left front wheel, and wherein the at least a second hydraulic motor is coupled to the right rear wheel to rotate the right rear wheel at the same velocity as it rotates the right front wheel. Each rear suspension may include a spring element coupled to and between the rear control arm and the chassis to apply a torque to the control arm, the spring element being fixed to the chassis at a point closer to the center of gravity of the vehicle than the pivot point of the rear control arm. The center of gravity may be determined with the vehicle unloaded.